1. Field of the Invention
This invention generally relates to a bi-directional power supply circuit, and in particular to a bi-directional power supply circuit for use in power generation systems to control the flow of electrical power to and from an electrical storage source.
2. Description of the Related Art
Various circumstances exist in which it is desirable to control flow of electrical power to and from an electrical storage source. For example, a battery may be used to store energy generated by a generator and to supply electrical power to a load when the generator is not activated or when the load power exceeds the power produced by the generator. In this regard, two separate circuits may be used to control flow of power between the electrical generating source and the electrical storage source. Specifically, one circuit may be used to convert electrical power produced by the generator into a voltage level appropriate for charging the battery and the other circuit may be used to convert electrical power from the battery to a voltage level appropriate for charging a power supply bus coupled to a load.
In U.S. Pat. No. 6,021,052, an attempt is made to use a single power conversion circuit and employ complex circuitry to selectively control direction of energy transfer in the desired direction. This approach, however, has a problem of undesired drop in output voltage during the direction transition period and complex methods are employed to minimize this effect. This prevents a completely seamless operation during change of direction. The usage of conventional feedback circuits in prior art devices for bus voltage control has several problems in stabilizing the bus voltage and thereby necessitates use of complex methods like non-linear response to error signals and mandatory use of large storage elements on bus to provide or store excess energy during load transients. Other problems with prior art devices include dependency on analog and logic components to implement control loops which are prone to temperature, tolerance and aging effects and difficulty in enhancing performance without changing components or component values.
According to one aspect of the invention, a system is provided for controlling the flow of electrical power between two sources. The system includes a circuit coupled between a first source and a second source and a controller subsystem coupled to the circuit. The circuit is capable of transitioning, in a continuous manner, between a first direction wherein electrical power flows from the first source to the second source and a second direction wherein electrical power flows from the second source to the first source. The control subsystem generates control signals to selectively activate switching elements of the circuit to control the direction and the amount of electrical power flowing through the circuit between the first and second sources.
In one aspect of one embodiment, the control subsystem of the present invention determines proper duration and timing of control pulses to selectively activate switching elements of subcircuits contained in a bi-directional power supply circuit. Additionally, a dominant feed-forward control is incorporated in the present invention which eliminates the need for large storage elements on a power bus and provides a fast response to load variations. As a result of these features, none of the selective mode control or complex logic is required, and a compact simple system model is formed thereby providing an effective way to smoothly control transition of energy flow path and/or direction between two or more energy sources. Such configuration enables loads to be connected to both energy sources simultaneously and the net current flowing between the two sources will be determined by the available energy and load demand at any instant of time, without any specific intervention of the controller to set direction.
In another aspect of one embodiment, a third source of energy can be coupled to the system without significantly changing the control logic.
In yet another aspect of one embodiment, the present invention computes, in real-time, voltage and current relationships to obtain net current rise or fall in a sub-circuit node of a bi-directional power supply circuit. This provides the system with an estimated value of currents in these sub-circuits before they actually occur, thereby achieving greater control over peak current amplitudes in a sub-circuit.